1. Field of the Invention
The present invention relates to a contactor employed to test the characteristics of electronic components such as semiconductor integrated circuits, and a test method using the contactor.
2. Description of the Related Art
In recent years, there have been increasing demands for reduction in the size and weight of electronic apparatuses such as personal digital assistants (PDAs), cellular phones, and digital cameras. This has also caused strong demands for reduction in the size and weight of electronic components used in these electronic apparatuses, such as semiconductor integrated circuits.
These demands are met by a rapid increase in semiconductor integrated circuit devices of a package form called CSP (Chip Size Package), according to which a package is configured to be substantially equal in size to an IC chip to be packaged. Package forms such as FBGA (Fine-pitch Ball Grid Array) and FLGA (Fine-pitch Land Grid Array) are typical examples of CSP. These semiconductor integrated circuit devices have minute external terminals arranged with fine pitches in order to be reduced in size.
IC packages other than CSP packages, such as QFP (Quad Flat Package) packages, also have minute external terminals arranged with fine pitches in order to meet the demands for reduction in size and weight.
In recent years, CPUs (Central Processing Units) for computers have become more integrated to have an increased number of external terminals. As a result, unlike the above-described CSP packages, the CPUs have become larger in size with finer external terminal pitches. BGA IC packages and LGA (Land Grid Array) IC packages, for instance, may be used in the CPUs. Further, there are demands for adapting the external terminals of these IC packages in shape and size as required by users so that the IC packages have better mountability. Accordingly, IC packages are offered in a variety of shapes with their external terminals varying in shape and size. As a result, a great many types of IC packages are on the market.
Further, in recent years, lead-free solder has been widely used as an outer plating material for the external terminals of IC packages from an environmental point of view. However, in today's transition period, both IC packages using lead-free solder and IC packages using conventionally employed lead solder are being produced.
As a result of the above-described realization of minute external terminals and fine external terminal pitches in CSP and other IC packages, the corresponding “miniaturization” is also required in contactors used to test these IC packages. Accordingly, contact pins provided in the contactors are required to be more complicated and minute in shape.
As described above, an increasing number of IC packages have come to have different external terminal shapes as a result of the diversification of IC packages. In consequence, various types of contactors with contact pins different in the shape of a contact part to be adapted to different IC packages should be prepared for conducting tests.
For the same reason, that is, in order to meet the demands for reduction in size and weight and an increase in integration, attempts have been made to realize smaller IC chips and electrodes. Further, in order to realize an increase in the number of electrodes for better electric characteristics, a rapidly increasing number of IC chips have employed an “area pad” or “area bump” electrode arrangement where the electrodes of a chip are arrayed in a lattice-like manner. Further, attempts have been made to realize fine electrode pitches in these IC chips. From an environmental point of view, lead-free solder is often employed in the area bump electrodes employed in these IC chips. In the present transition period to switch to lead-free solder, and both IC packages using conventional solder and IC packages using lead-free solder are being produced by semiconductor manufacturers. Like the above-described CSP and other IC packages, IC chips also require contactors to have complicated and minute shapes adapted to the electrodes of the IC chips.
FIG. 1 is a diagram showing a contactor 1 having conventional contact pins. The contactor 1, which is used to test the characteristics of a BGA-type IC package 2, includes multiple contact pins 3. Each of the contact pins 3 has a contact electrode 4a contacting a corresponding one of external electrodes 2a of the IC package 2 and an electrode 4b connected to a corresponding terminal (not graphically represented) of a test circuit board 5. A metal coil spring 6 is provided between the contact electrode 4a and the electrode 4b so as to electrically connect the contact electrode 4a and the electrode 4b and to urge the contact electrode 4a and the electrode 4b in opposite directions. This urging (spring) force of the coil spring 6 presses the contact electrode 4a against the external electrode 2a of the IC package 2 so that a suitable contact pressure is generated.
According to this configuration, each terminal of the test circuit board 5 is electrically connected to the corresponding external electrode 2a of the IC package 2 through the corresponding contact pin 3, so that an electrical test can be conducted on the IC package 2. Each contact pin 3 is an integrated unit with the contact electrode 4a and the electrode 4b being fixed to the ends of the coil spring 6. The contact pins 3 are arranged in the contactor 1 in accordance with the arrangement of the external electrodes 2a of the IC package 2. Accordingly, it is impossible to replace each contact electrode 4a as a unit.
The contact part of the contact electrode 4a of each contact pin 3 may be shaped like a crown, an inverse cone, a flat cylinder, or a hemisphere. In order to be adapted to external terminal shapes and sizes of IC packages, the contact pins 3 should be prepared in various types different from one another in the detailed dimensions of the contact part.
For instance, as a contactor used to test the characteristic of the BGA IC package 2, Japanese Laid-Open Patent Application No. 2000-221236 discloses a configuration where the positions corresponding to electrodes on a contact sheet are pressed from the lower side so that the electrodes are pressed against the electrodes (solder balls) of an IC package positioned above the contact sheet.
As another conventional contactor, a contactor 11 having contact pieces is shown in FIG. 2. The contactor 11 shown in FIG. 2, which is used to test the characteristics of a QFP-type IC package 12, includes multiple spring electrodes 13. Each spring electrode 13 has a contact end 14a contacting a corresponding one of external electrodes 12a of the IC package 12 and an electrode end 14b connected to a corresponding terminal (not graphically represented) of a test circuit board 15. A spring part 14c is provided between the contact end 14a and the electrode end 14b so that the contact end 14a, the electrode end 14b, and the spring part 14c are integrated.
The electrode end 14b is inserted into an opening in the test circuit board 15 to be fixed thereto. The spring part 14c, which has a curved shape, is elastically deformable. Therefore, the elastic deformation force of the spring part 14c presses the contact end 14a against the external terminal 12a of the IC package 12 so that a suitable contact pressure is generated.
According to this configuration, each terminal of the test circuit board 15 is electrically connected to the corresponding external electrode 12a of the IC package 12 through the corresponding spring electrode 13, so that an electrical test can be conducted on the IC package 12. Each contact end 14a is integrated with the corresponding spring electrode 14c. Accordingly, it is impossible to replace only the contact end 14a as a unit.
When an IC package is pushed into such a contactor as described above to be mounted thereon using an automatic machine such as a test handler in a mass production process, “parallel pushing” may not be performable depending on factors such as parallelism on the automatic machine side, board parallelism, and board deflection. This is particularly true in IC packages with a large shape, a large number of external terminals, and fine pitches, such as CPUs.
Accordingly, since contact pins normally show their optimum spring characteristics when they are pushed straight, a normal operating state cannot be obtained, so that contact stability cannot be obtained. Further, springs provided in the contactor are likely to have a shortened useful service life.
Normally, gold, solder, or palladium is used as outer plating material for the external terminals of an IC package. When the external terminals come into contact with the contact electrodes of the contact pins of the contactor, the outer plating of the external terminals may be transferred to the contact electrodes. Particularly, the deposition of transferred solder plating on the contact parts of the contact pins causes a problem. That is, the surface of the solder plating transferred to the contact parts is oxidized into an insulating foreign material, thus resulting in poor contact.
Further, the deposition of foreign material such as dust in a laboratory or the residual resin of an IC package on the contact parts of the contact pins also results in poor contact.
External terminals using lead-free solder, for which there have been increasing demands for environmental reasons, do not permit attachment or mixture of lead in light of the reasons for the demands. At present, however, lead may be attached to the external terminals of even a semiconductor integrated circuit device that meets the “lead-free” demand. Products using lead-free solder and products using the conventional lead solder are both being distributed. Therefore, in a contactor for measuring and testing an IC package, lead transferred to and deposited on the contact parts of the contactor when the contactor comes into contact with external terminals using lead solder may adhere to external terminals using lead-free solder when the contactor next comes into contact therewith.
Further, when a problem occurs in a BGA-type IC package after the IC package is once mounted on a board, an electrical test should be conducted on the IC package after the IC package is removed from the board. At this point, if the IC package has, for instance, solder balls as external terminals, each solder ball of the IC package after being removed from the board is not in its original state with a portion or even a substantial part thereof missing. Accordingly, the external terminals of the IC package removed from the board vary in shape and size.
A contactor used at the time of mounting the IC package on the board cannot be used for the external terminals (or where the external terminals used to be) of the IC package removed from the board. Accordingly, it is only after the same type of solder balls as the original ones are provided on the IC package removed from the board that a test is conducted using the contactor.
When an IC package is newly manufactured, solder balls are provided to the IC package using an automatic machine for providing solder balls. However, solder balls are manually provided one by one to an IC package that is removed from a product in which the IC package has been incorporated. This operation of providing solder balls requires a lot of time and effort.
The same problems as described above, that is, unstable contact in the case where “parallel pushing” is not performable and a shortened useful service life of springs, are likely to occur between contact electrodes on the test circuit board side and the terminals of a test circuit board. Further, a contactor comes into contact with the test circuit board every time the contactor is used. The contact with the terminals of the board is likely to cause damage such as concave scratches and plating peeling to the contactor. This often results in poor contact.
The above-described problems such as unstable contact in the case where “parallel pushing” is not performable, a shortened useful service life of springs, the transfer of chip outer plating and resultant poor contact, and the attachment of lead solder to and the mixture of lead solder into a lead-free product also occur in IC chips. U.S. Pat. No. 4,027,935 discloses a contactor contacting the external electrodes of a chip. The contactor includes contacts (contact pins) that are buckling spring electrodes whose contact parts buckle to move horizontally at the time of contact. Accordingly, contact deficiency and damage to a terminal of a circuit board are likely to occur at the time of contact. Further, since contact displacement is limited, unstable contact in the case where “parallel pushing” is not performable is likely to occur. Further, the material of the contact pins is not freely selectable since priority is given to the spring characteristic of the contact pins. Furthermore, since the contact pins are formed from a plate material by etching or molding, their end shape, or contact electrode shape, is not freely selectable. For the reasons stated above, the above-described problems are likely to occur.